The present invention relates to self-contained, automatic fire protection systems and more particularly systems adapted for use in engine compartments of marine craft and the like.
Fire protection systems are commonly used in the engine compartments of marine craft. Such systems automatically actuate to extinguish an engine compartment fire. Typical systems include a pressure vessel, cylinder or bottle filled with a extinguishing material or agent. A typical agent is Halon 1301 which is manufactured by E. I. DuPont de Nemours. The extinguishing agent is stored under pressure in a liquid state within the pressure vessel. A pressurizing gas such as nitrogen may also be contained within the bottle. The system includes an actuator which includes a nozzle and a thermally responsive trigger. When a predetermined temperature is reached, the trigger releases and the agent is discharged.
Prior fire extinguishing systems may also include a pressure switch used to initiate an engine shutdown sequence. Initiating engine shutdown is particularly important when the marine craft employs diesel engines. Upon discharge of the Halon agent from the fire extinguishing system, the engine's normal aspiration of air from its enclosure or engine room lowers the concentration of the agent. This may prevent full extinguishment or result in a reflash of the fire. In addition, aspiration of the Halon agent into the engine creates Halon breakdown products. The breakdown products result when the agent is aspirated into a diesel, as opposed to a gasoline internal combustion engine, due to the higher combustion pressures and temperatures present. Gasoline engines are stopped immediately upon reaching a 5% concentration of Halon 1301 agent. A diesel engine, however, may require in excess of a 30% Halon 1301 concentration to stop without external shutdown procedures. When Halon 1301 agent is allowed to break down into its components inside an operating diesel engine, the exhaust from the engine will contain hydrogen fluoride and hydrogen bromide in potentially toxic quantities. Failure to initiate immediate engine shutdown may create the potential, therefore, for a reflash of the fire and a health hazard due to the release of toxic breakdown products.
Responsiveness problems are experienced with present engine shutdown systems in a Halon 1301 fire extinguisher. The pressure switches operate based upon a decrease in pressure within the fire extinguishing system. The Halon agent is a liquified, compressed gas, its discharge pressure curve is fairly constant until substantially the entire agent has been discharged from the bottle or cylinder. In some systems, engine shutdown may not be initiated until up to eight seconds after actuation of the automatic fire protection system. A need exists, therefore, for a self-contained fire protection system and/or pressure switch arrangement which provides faster response times.